This application is based upon Japanese Patent Application No. Hei 11-184,467, filed on Jun. 29, 1999.
1. Field of the Invention
The present invention generally relates to engine decompression systems to assist with starting higher compression engines. More particularly, the present invention relates to such systems having compact component arrangements for use on engines that may be positioned within smaller engine compartments.
2. Description of Related Art
Snowmobiles are popular land vehicles that are used primarily in the winter and in cold and snowy conditions. These conditions can sometimes make certain vehicle operations, such as starting, more difficult.
Snowmobile designers recently have been implementing four stroke engines in order to reduce emissions during engine operation. Typically, however, the size and complexity of four cycle engines is greater than the size and complexity of conventional two cycle engines. Moreover, four cycle engines-use exhaust valves and intake valves that are timed to increase compression within the engine. In particular, while two cycle engines use the piston to open and close the ports into the combustion chamber, four cycle engines use valves to control flow through the ports. Thus, if the valves operate normally, larger compression ratios can be obtained within the combustion chamber as compared to two cycle engines.
The higher compression ratios make manual or pull starting the engine more difficult. The increased difficulty is caused by the need to manually provide the movement of the pistons that result in the higher compression ratio. Not all riders may be strong enough to achieve the necessary forces. The higher compression ratios needed are further accentuated by cold climates, such as those in which snowmobiles operate. Thus, four cycle snowmobile applications present significant pull resistance and starting problems due to comparatively high compression pressure and cold air operation.
A need, therefore, exists for a decompression system that makes engine starting easier. Also, a need exists for a decompression system adapted for use in a snowmobile, making starting easier in cold climates. Moreover, a need exists to create a decompression system that will minimize the size of the four cycle engine so that the snowmobile vehicle size can be minimized.
Accordingly, one aspect of the present invention involves a snowmobile comprising a frame assembly with an internal combustion engine mounted to the frame assembly. The engine comprises a cylinder block defining a cylinder bore, a cylinder head assembly fixed at one end of the cylinder block enclosing one end of the cylinder bore and a connecting rod pivotally connected to a piston and a crankshaft. The crankshaft is rotatably journaled and driven by the piston through the connecting rod.
The piston, the cylinder bore and the cylinder head form a combustion chamber. At least one exhaust port is defined in the cylinder head with at least one exhaust valve being provided in the exhaust port. The exhaust valve selectively allowing fluid communication between an exhaust system and the combustion chamber through the exhaust port. A decompression mechanism is mounted on the cylinder head and is capable of actuating the exhaust valve from a normal operating condition to a decompression operating condition. A lever is mounted on the frame assembly and connected to the decompression mechanism. The lever is capable of actuating the decompression mechanism from a first position to a second position with the first position corresponding to the normal operating condition and the second position corresponding to the decompression operation condition.
Another aspect of the present invention involves a snowmobile comprising a frame assembly with an internal combustion engine having a cylinder block defining at least two cylinder bores. A cylinder head assembly is fixed at one end of the cylinder block and encloses one end of the at least two cylinder bores. At least two connecting rods are pivotally connected to at least two corresponding pistons. A crankshaft is rotatably journaled and is driven by the at least two pistons through the at least two connecting rods. The at least two pistons, the at least two cylinder bores and the cylinder head form at least two combustion chambers. At least one exhaust port is defined in the cylinder head corresponding to each of the at least two cylinder bores. An exhaust valve is provided in each of the exhaust ports. A cam shaft has a cam lobe for actuating each of the exhaust valves with the exhaust valves allowing fluid communication between the exhaust ports and the combustion chambers. A decompression mechanism is mounted on the cylinder head with the decompression mechanism being capable of actuating the exhaust valves from a normal operating condition to a decompression operating condition. The decompression mechanism comprising a bracket affixed to the cylinder head. A first support shaft is journaled on the bracket and a second support shaft is journaled on the bracket. A cam is fixed to the first support shaft and a cam lever also is fixed to the first support shaft. A pivotal lever is fixed to the second support shaft and is in sliding connection with the cam at a first pivotal end and is in pressing connection with the exhaust valve at a second pivotal end. A lever is capable of actuating the decompression mechanism and is remotely located relative to the engine.
A further aspect of the present invention involves a land vehicle comprising a frame and a body. An engine compartment is defined within at least a portion of the body. At least one steerable member supports the frame with a steering handle being connected to the steerable member. An engine is mounted to the frame within the engine compartment. The engine comprises a cylinder body defining a cylinder bore. An exhaust passage extends from the cylinder bore. An exhaust valve is positioned along the exhaust passage and comprises a tappet. An exhaust cam shaft operatively contacts the exhaust valve. A decompression mechanism comprises a lever selectively contacting the exhaust valve with the lever being operatively connected to an actuator mounted outside of the engine compartment.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiment which follows.